I started my opening preparation only when I joined a chess club. My first opening book was The Batsford Chess Openings book 2 which has many different openings in it well explained by well renowned British Chess Author GM Raymond Keene. I saw all the mounds of theory with the 1 d4(Queens Pawn Opening) and 1 e4(Kings Pawn Opening) and decided as White to play something with less theory. I immediately hit upon the idea of playing the Reti opening i.e. 1 Nf3 and I got good results with it. 
As Black I played the Caro-Kann (1 e4 c6) and the Slav (1 d4 d5 2 c4 c6) basing my strategies around a quick c6 move. Now as White I found that after 1 Nf3 d5 2 c4 d4 I got a cramped position so after a period of a few years playing it I decided to move on to experiment with 1 g3 (The Benko-Larsen Opening), the Kings Indian Attack i.e.(1 g3 2 Bg2 3 Nf3 or 3 c4) and then read up on playing 1 d4 d5 2 Nc3 Nf6 3 Bg5 (The Veresov Opening) but it wasn't until I decided to look at 1 c4 (The English Opening) that I found a permanent Opening system, which I have stuck with so far, for 24 years. I am writing a book on my opening repertoire which will be published as web pages on this site. I am still working on it but it can be seen below:-
  1. The English Opening

  2. The Alekhine Defence

  3. The Pirc Defence

  4. The Grunfeld Defence

  5. The King's Indian Defence

  6. The Queen's Gambit Accepted

  7. The Sicilian Dragon

I found also their was a reason why, as Black, c6 isnt played  early and that is because it hampers Blacks Light Squared Bishop and I found I was loosing or drawing games which I shouldn't with these openings. I then decided to play as Black a system based around a Fianchettoed Bishop on the King side i.e. I played The Modern (1 e4 g6), The Pirc (1 e4 g6 2 d4 Bg7 3 Nc3 Nf6) and the Kings Indian Defence (1 d4 g6 2 c4 Bg7 3 e4 d6 4 Nc3 Nf6). Although I got good results with this system of development I finally decided to play after around 3 years of that system, The Alekhine Opening (1 e4 Nf6) this is very provocative, another provocative opening I decided to play, in 1998, against 1 d4 was The Grunfeld Defence (1 d4 Nf6 2 c4 g6 3 Nc3 d5).
I still play both openings today but have included a few openings to play against lower graded opponents which are less theoretical like The Queens Gambit Accepted (1 d4 d5 2 c4 dc) and the unusual Dunst Opening (1 Nc3) . I also have learnt and am going to learn about the Sicilian Dragon, which is highly theoretical.